Cyclopropene activation via I(I)/I(III) catalysis: Proof of principle and application in direct tetrafluorination

Preliminary validation of cyclopropene activation by an I(I)/I(III) catalysis manifold is disclosed to enable the direct tetrafluorination of 3,3-diarylcyclopropenes. This transformation occurs through the in situ generation of ArI(III)F2, with inexpensive iodobenzene, amine·HF complexes and Selectfluor® serving as catalyst, fluoride source and oxidant, respectively. Leveraging this approach, it has been possible to generate four C(sp3)-F bonds in a single operation (up to 44%). A Hammett study revealed that the reaction has a very narrow tolerance window with respect to the p-substituent of the aryl groups. Through a process of reaction deconstruction, a mechanism involving two discrete catalytic processes is proposed. Whereas the first cycle results in the ring opening fluorination of the 3,3-diarylcyclopropene, the second proceeds via a fluorination/phenonium ion rearrangement to liberate a tetrafluorinated diarylethane. This study adds hypervalent iodine catalysis to the plenum of strategies that facilitate cyclopropene activation

Intermolecular interactions in blends of poly(vinyl alcohol) with poly(acrylic acid): 2. Correlation between the states of sorbed water and the interactions in homopolymers and their blends

Water-polymer interactions have been studied by d.s.c. and FTi.r. in water vapour-saturated poly(vinyl alcohol), poly(acrylic acid) and their blends before and after thermal treatment (0.5 h at 180°C). The 3600-3000 cm-1 (OH stretching), 1800-1700 cm-1 (C=O stretching) and 1700-1600 cm-1 (HOH bending) regions have been used. Water-polymer and polymer-polymer interactions which are respectively formed and destroyed in the presence of water have been identified. For this purpose, subtraction of the spectrum of dry samples from the spectrum of water-saturated films has been performed. Changes in crystallinity of poly(vinyl alcohol) were also measured by FTi.r. D.s.c. has been used to confirm the strength of water-polymer interactions and to demonstrate changes in the miscibility of polymer components. Copyright © 1996 Elsevier Science Ltd.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Intermolecular interactions in blends of poly(vinyl alcohol) with poly(acrylic acid)-1. FTIR and DSC studies

The i.r. spectra and the melting behaviour of blends of poly(vinyl alcohol) (PVAI) and poly(acrylic acid) (PAA) have been studied as a function of blend composition. Replacement of H-bonding interactions in pure PAA and PVAI by intermolecular interactions has been proved by analysis of the OH and CO stretching region in the i.r. spectra. The efficiency of these intermolecular interactions results in a rapid decrease of the crystallinity of PVAI when the PAA content increases and its complete supression when the PAA content equals or exceeds 50 wt%. A very high negative value has been obtained for the interaction parameter by measurement of the melting point depression. © 1992.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Blue-emitting bolaamphiphilic zwitterionic iridium(iii) complex

Aggregation induced emission is a very interesting phenomenon that recently has attracted a lot of interest. Most of the examples deal with organic molecules or flat metal complexes. Here we demonstrate that, by design, even iridium compounds can display this process without shifting the emission energy. In order to enhance the aggregation properties we have focussed on amphiphilic complexes. We report the synthesis and photophysical characterisation of a blue-emitting bolaamphiphilic zwitterionic Ir(iii) complex and an analogous cationic amphiphilic compound, used as a reference. The bolaamphiphile exhibited blue (\u3bbmax = 450 nm) emission in dilute, deaerated solution with a photoluminescence quantum yield (PLQY) of 22%, similar to the related cationic amphiphilic complex. The bolaamphiphile displayed significant emission enhancement in the solid state, with an emission quantum yield that reach 52%. Interestingly, the emission of the cationic analogue suffers from aggregation quenching in the solid state, (PLQY = 3%) as is common for these type of complexes. A correlation between the photophysical data and the arrangement in the solid state is discussed

Tuning the structural and photophysical properties of cationic Pt(II) complexes bearing neutral bis(triazolyl)pyridine ligands

The emission properties of a series of cationic Pt(II) complexes bearing neutral tridentate 2,6-bis-(1H-1,2,3-triazol-5-yl)pyridine and monoanionic ancillary ligands (Cl- or CN-) are described. By varying the substitution pattern on the 1,2,3-triazole moieties of the tridentate luminophore and the nature of the ancillary ligand, we were able to tune the intermolecular interactions between the complexes and therefore the electronic interactions between the metal centers. Indeed, all the compounds possessing Cl- as ancillary ligand are nonluminescent at room temperature, while the complexes containing CN- are luminescent. Interestingly, the \u3c0-accepting nature of this ancillary ligand induces Pt(II)-Pt(II) interactions irrespectively of bulky substitution patterns on the tridentate ligand

Nucleoside macrocycles formed by intramolecular click reaction: efficient cyclization of pyrimidine nucleosides decorated with 5'-azido residues and 5-octadiynyl side chains

Copper(I)-promoted "click" cyclization in the presence of TBTA afforded nucleoside macrocycles in very high yields (≈70%) without using protecting groups. To this end, dU and dC derivatives functionalized at the 5-position of the nucleobase with octadiynyl side chains and with azido groups at the 5’-position of the sugar moieties were synthesized. The macrocycles display freely accessible Watson–Crick recognition sites. The conformation of the 16-membered macrocycle was deduced from X-ray analysis and 1H,1H-NMR coupling constants. The sugar conformation (N vs S) was different in solution as compared to the solid state

Bidentate NHC pyrozolate ligands in luminescent platinum(ii) complexes

A bidentate C^N donor set derived from an N-heterocyclic carbene (NHC) precursor linked to a trifluoromethyl (CF3) functionalized pyrazole ring is described for the first time. The ligands have been employed to prepare four new phosphorescent complexes by the coordination of platinum(ii) centres bearing cyclometalated phenyl-pyridine/triazole-pyridine chelates. The electronic and steric environments of these complexes were tuned through the incorporation of suitable substituents in the phenyl-pyridine/triazole-pyridine ligands, wherein the position of the phenyl-ring substituent (a CF3 group) also directs the selective adoption of either a trans or a cis configuration between the CNHC and the Cphenyl donor atoms. Molecular structures obtained by X-ray diffraction for three of the complexes confirm a distorted square-planar configuration around the platinum centre, and DFT calculations show that the substituents have a significant influence on the energies of the frontier orbitals. Moreover, a platinum(ii) complex featuring the new bidentate NHC^pyrazolate ligand and a bulky adamantyl functionalized pyridine-triazole luminophore was observed to be highly emissive and exhibiting a sky-blue luminescence (\u3bbEm = 470 nm) with photoluminescence quantum yields as high as 50% in doped PMMA matrices. A complete photophysical investigation of all of the complexes in solution as well as in the solid state is herein reported

Leveraging the n→π* Interaction in alkene isomerization by selective energy transfer catalysis

Examples of geometric alkene isomerization in nature are often limited to the net exergonic direction (ΔG°0) comparatively under-represented. Inspired by the expansiveness of the maleate to fumarate (Z→E) isomerization in biochemistry, we investigated the inverse E→Z variant to validate nO→πC=O* interactions as a driving force for contra-thermodynamic isomerization. A general protocol involving selective energy transfer catalysis with inexpensive thioxanthone as a sensitizer (λmax=402 nm) is disclosed. Whilst in the enzymatic process nO→πC=O* interactions commonly manifest themselves in the substrate, these same interactions are shown to underpin directionality in the antipodal reaction by shortening the product alkene chromophore. The process was validated with diverse fumarate derivatives (>30 examples, up to Z:E>99:1), including the first examples of tetrasubstituted alkenes, and the involvement of nO→πC=O* interactions was confirmed by X-ray crystallography